Poor prognosis in pancreatic cancer is due in part to poor response to the current standard of care (gemcitabine, a cytidine nucloeside analog). Our preliminary data establish a novel, widely-prevalent mechanism of resistance to fluoropyrimidines whereby the Hypoxia-Inducible Factor1 (HIF1) alpha-induced glycolytic flux leads to a corresponding increase in the pyrimidine biosynthetic pathway to enhance the intrinsic levels of cytidine. Such increased levels of cytidine/dCTP diminish the effective levels of gemcitabine and 5FU (in FOLFIRINOX) through molecular competition or dilution. Our data also indicate existance of a bidirectional tumor-stromal metabolite flux that may facilitate tumor/stromal cell survival under low nutrient conditions, promote desmoplasia, increase metabolite flux into pyrimidine biosynthetic pathway, and result in decreased chemotherapy sensitivity. Thus, we propose to determine if combining gemcitabine/FOLFIRINOX therapies with digoxin (to target HIF1 alpha) or Leflunomide (to target pyrimidine biosynthesis) will diminish fluoropyrimidine therapy resistance in pancreatic cancer patients (AIM 1). Additionally, we will employ 18FFDG- PET imaging in pancreatic cancer patients to predict the resistance status of the tumor against pyrimidine analogs (AIM1). We will also investigate if cytidine levels in pancreatic tumors/biofluids may serve as potential biomarkers for chemotherapy responsiveness in pancreatic cancer patients (AIM2). Furthermore, we will investigate if tumor-stromal metabolite exchange facilitates stromal cell survival and desmoplasia in tumor models, and increased pyrimidine biosynthesis and diminished gemcitabine responsiveness in tumor cells (AIM3). We predict that our proposed improvement to current chemotherapy strategies will improve survival in pancreatic cancer patients by increasing the efficacy and/or decreasing the toxicity, by requiring smaller doses, of chemotherapy strategies that employ gemcitabine and/or 5FU.